1. Field of the Invention
The present invention relates to a power transmission device mounted to a vehicle, and more particularly to a power transmission device that reduces vibration generated from a composite gear member including internal teeth engaged with a pinion gear of a planetary gear device, in order to function as a ring gear of the planetary gear device, and external teeth engaged with another gear.
2. Description of Related Art
As one example of a power transmission device mounted to a vehicle, there is a power transmission device which is provided with a composite gear member including internal teeth engaged with the pinion gear of a planetary gear device, in order to function as a ring gear of the planetary gear device, and external teeth engaged with another gear. A ring gear of such a planetary gear device is described in Japanese Patent Publication No. JP-B2-7-65657 (see reference numeral 13 in FIG. 2 of Japanese Patent Publication No. JP-B2-7-65657).
In general, a planetary gear device comprises a sun gear, a ring gear and a plurality of pinion gears disposed between the sun gear and the ring gear. The pinion gears are arranged equiangularly with each other. When the planetary gear device is driven, an engagement reaction force is generated from contact portions between the engaged teeth of the gears. Because the engagement reaction force is equally exerted on the respective pinion gears, it was known that eccentricity of the planetary gear device is automatically reduced by the engagement reaction force, That is, a so-called aligning operation occurs.
However, in the power transmission device disclosed in Japanese Patent Publication No. JP-B2-7-65657, which is provided with the composite gear member including the external teeth engaged with another gear, in addition to the engagement reaction force generated in the planetary gear device, an additional engagement reaction force is generated from the external teeth engaged with the other gear of the composite gear member. Consequently, there is a problem that, by the engagement reaction force generated from the external teeth, the balance of the engagement reaction force in the planetary gear device may not be maintained. Thus, vibrations are easily induced.